On the Extinction of Species

The Dodo used to walk around,And take the sun and air.The sun yet warms his native ground--The Dodo is not there!

The voice which used to squawk and squeakIs now for ever dumb--Yet may you see his bones and beakAll in the Mu-se-um.

The possibility that species can disappear from a continent was realized 300 years ago, and only 100 years later the research by French naturalist Cuvier showed that species in fact can disappear completely - gone extinct forever.Cuvier not only recognized extinction, but used the disappearance and appearance of fossils in the stratigraphic column of the Tertiary strata of France to divide the history of earth in various, successive faunas, every one destroyed by a revolution of the earth's surface (the chosen term to name these changes is clearly influenced by the French revolution of 1789-1799). After the catastrophic event earth got soon repopulated with new species of organisms - however this spontaneous, sudden generation wasn't addressed by Cuvier, there was a gap filled by a possible supernatural creation.Geologist Charles Lyell, who tried to establish geology as serious science without such miraculous interference, tried to deny, and then minimize the role of these single extinction events in earth history. Lyell's hostility against extinction in general was also a consequence of his deny of organic progression (as most naturalists at these times), implying that organism, or even entire animal classes could go lost, lead to the conclusion that new species must somehow provided new, and without claiming for divine creation only a transmutation of species would be possible.Lyell accepted a local extinction of species as consequences of climatic change, concurrence and human activity (like in the case of the Dodo), however these local extinctions were reversible, surviving animals could spread again from a refuge when the conditions were favourable again (…no species may be lost…page 193 LYELL 1842). The apparent distinct succession of fossil faunas, so Lyell, was an artefact of former distribution of land and sea, the missing preservation of land-organisms in marine deposits and the general incompleteness of the geological record. Lyell could show that various sharp boundaries between marine and terrestrial strata, as proposed in Cuviers model of the Tertiary of France, were in fact separated by sediments deposited in lakes and rivers, there was no sudden change, but by slow rise the sea became first a swamp and later land. Also the "worldwide" limits of Cuvier ended in the Auvergne - there were no signs that this volcanic region was covered by sea in the Tertiary.Cuvier´s Catastrophism soon became replaced by Lyell's Uniformitarianism.

Charles Darwin became strongly influenced by the geology of Lyell, observing at his first stop during the Voyage of the Beagle on the Cape Verde islands (January 16, 1832) sediments enclosed by lava flows and raised above the sea level, but with fossils similar to the shells in the sea nearby (implying no substantial change of acting natural forces and habitats over time), he applied the principles proposed by Lyell and became convinced of the slow, minute and gradual changes of earth surface.When Darwin published his "On the Origin of Species", Catastrophism seemed long dead.Darwin adopted his gradual change model of earth on the biological evolution of life; evolution did not need catastrophic events to explain extinction.He stated that one of the main factors contributing to the evolution of organisms was perpetual concurrence in an overcrowded world, catastrophic events (like a drought) could occur, killing many individuals, but nevertheless this local and rare events were outstripped by the much more significant role of long-lasting, gradual natural selection, where the less adapted organism became extinct by the concurrence, and success of the modified variations.As Lyell, Darwin considered the apparent sudden transitions of fossil faunas as an artefact of the imperfection of the geological record - in principle he denied mass extinctions as we today see it in the stratigraphic record.

But there were some theories about "evolution" and "extinction". Darwin and Wallace were both strongly influenced and based their definitive theory of 1859 also on thoughts and works of other naturalists; transmutation of species was a concept discussed at these times.In 1831 the Scottish horticulturalist Patrick Matthew (1790-1874) published in an appendix of his book "Naval Timber and Arboriculture" a theory about transmutation in nature, which resembles the concept of variation, concurrence and selection adopted later by Darwin and Wallace:

"There is a natural law universal in nature, tending to render every reproductive being the best possibly suited to its condition…As the field of existence is limited and pre-occupied, it is only the hardier, more robust, better suited to circumstance individuals, who are able to struggle forward to maturity…"(from RAMPINO 2010)

Matthew however, in explaining the forces that influenced this process, gave to catastrophic events a significant role, maintaining that mass extinctions were crucial to the process of evolution by eliminating concurrence, and enabling organism to radiate in the now "free world":

" ..all living things must have reduced existence so much, that an unoccupied field would be formed for new diverging ramifications of life... these remnants, in the course of time moulding and accommodating ... to the change in circumstances."(from RAMPINO 2010)When published, Matthew's book raised little interest, and even if both Darwin and Wallace later recognized his contribution, Matthew "evolutionary" interpretation of the geological record, with extinction events, became almost forgotten.

After "Origin of Species" the main interest of palaeontologists focused on the evolution of species, rather then their extinction.Despite proclaiming to accept Darwin's evolution, many naturalists of the second half of the 19th century struggled with the idea of "random" natural selection (intended as a process without end destination, especially not the human species). This led to the concept of a sort of guided evolution, resembling much more the transmutation of Lamarck, where single species pass trough a development process, with generation, spreading, adaption and finally overspecializiation or degeneration, leading them to extinction. The aberrant ammonites of the Cretaceous sea and the gigantic dinosaurs were seen of such examples of overdevelopment.

The idea of a distinct extinction event acting worldwide, and then forcing evolution, remained a neglected theory for the rest of the 19th century, and most of the 20th century, even when large scale geological changes, as for example an ice-age, were accepted in the scientific community.Maybe the idea that terrestrial phenomena could endanger life on earth seemed to threatening? It was so that an extraterrestrial phenomenon brought the role of catastrophes in earth's evolution back to discussion.